I am looking for the designation and specifications for the threads at the base of a standard toilet valve for residential applications. This is the thread that mates with the water line just below the toilet reservoir on most toilets.

This should be the same thread used for common threaded water lines.

It appears to be a straight thread, but does not match the size of any pipe threads.

I was curious why several people have posted that this is not a straight thread. I have a guess as to why that is happening - I probably did not explain myself very clearly.

I was looking for the thread that is used at the base of the fill valve column within residential toilet tanks. This is the thread that runs through the floor of the toilet tank and has a water line attached on the end.

Because this thread has to go through the floor of the toilet tank (with varying thickness), get secured with a nut against the floor of the toilet tank, and have a water line attached at the end, it is a long, straight thread.

Curious as to why the question was asked. Most people looking to do a repair or install are satisfied without the specs of the fill valve spud, but you are asking for such detail as if you are preparing to invent or fabricate an appurtenance for toilets.
Like I said, just curious.

Curious as to why the question was asked. Most people looking to do a repair or install are satisfied without the specs of the fill valve spud, but you are asking for such detail as if you are preparing to invent or fabricate an appurtenance for toilets.
Like I said, just curious.

You are correct. I am designing a new product for a client. This product will take the place of the "fill valve spud" (I just learned a new term), so I needed to have the detailed specs. I have modeled this thread into a molded body for the new product.

When the product is available on the market, I will post a follow up to this forum. At the moment, I am obliged to not discuss my client's upcoming product.

Maybe I can give some advice that will help you in your design. I have a friend who is an independent patenting agent and we have had many conversations about the plumbing industry. I have seen a number of widgets that have been patented, prototyped and produced for the plumbing world. When a plumber like me has a service call and discovers one of these items attached to a toilet supply, fill valve, overflow, ect. we focus on it as the reason for the service call. No problems existed before the attachment or purchase and after a short period of time the troubles start to show up. Upon removal of the appurtenance, life goes back to normal.
So my advice is this. Be sure the item is time tested and true to its function. Be sure it does not contribute to or create a new problem. If there is no practical need for it, the plumbing community is not likely to welcome or purchase it...it becomes an added expense and just another thing to break/leak and cost us all more money. Use durable materials and go above the minimum specs on design, early failure of a product will put it into a grave fast. (We all remember what happened to polybutylene epoxy when exposed to chlorinated water).
If you can find a plumber to test and critique the prototype, do so with non-disclosures signed, of course. We can be great cynics, but also will praise without bias.

If you are successful, we would all love to see a new product that continues to push the plumbing industry through the 21st century.

Nice, havasu. That would be better than another 'green' water saver valve. Reduces the volume of water flowing into the toilet tank. Problem is, the tank volume is the tank volume. It still requires the same amount of water to flush. Same thing goes for the water savers for filling the bowl via the overflow tube. Most people end up complaining that their toilet bowl doesn't clear well. Creating a solution for a problem that doesn't exist.lol.